Rear screen projection device provided with luminous markings

ABSTRACT

An improved rear screen projection device is disclosed. The projection device includes a front mounted source of non-visible light directed at indicia or reference markings on the screen. The markings are formed from a luminous paint or ink which glows under the nonvisible light thereby enabling the visibility of the markings to be vastly improved without effecting the resolution of the projected image. The ink is transparent or translucent so as not to interfere with any portion of the projected image.

United States Patent [191 Fox REAR SCREEN PROJECTION DEVICE PROVIDEDWITH LUMINOUS MARKINGS James E. Fox, Northport, N.Y.

Assignee: Diamagnetics, lnc.', Freeport, NY.

Filed: July 7, 1971 Appl. No.: 160,365

Inventor:

US. Cl ..250/72 Int. Cl. ..G0ld 7/06 Field of Search ..250/71 R, 72

References Cited UNITED STATES PATENTS 1/1970 Glowa et 51. ..250/72 [451May 22, 1973 Primary Examiner.lames W. Lawrence Assistant Examiner-DavisL. V

A ttorney- David S. Kane, Daniel H. Kane, Philip T. Dalsirner et al.

[ ABSTRACT An improved rear screen projection device is disclosed. Theprojection device includes a front mounted source Of non-visible lightdirected at indicia or reference markings on the screen. The markingsare formed from a luminous paint or ink which glows under the nonvisiblelight thereby enabling the visibility of the markings to be vastlyimproved without effecting the resolution of the projected image. Theink is transparent or translucent so as not to interfere with anyportion of the projected image.

3 Claims, 2 Drawing Figures BACKGROUND OF THE INVENTION Rear screenprojection devices find application in many areas of industry, commerce,and education. Examples of such devices include still and moving pictureprojectors, microfilm readers, comparators, and shadow graphs to namejust a few. These devices all have in common the fact that an immage isprojected onto the rear of a transparent or translucent screen forviewing from the front.

It is often necessary for the viewer of the rear screen projector tocompare the viewed image to some fixed markings on the screen. Themarkings may be simple, such as a set of cross hairs, measuring scale,or the like or they comprise a complex pattern which the contours of theviewed image are to follow. In either case, it is desirable for both themarkings and image to have maximum fidelity and resolution. This is notpossible with conventional rear screen projection devices since the rearscreen lighting which is necessary for the projected image detracts fromthe fixed markings while any front lighting of the screen wouldadversely effect the resolution of the projected image. Also, it isundesirable for the markings to interfere with the outline of theprojected image by blocking out a portion of the same. This isparticularly important where the dimensions of the viewed image arecritical.

l-leretofore, it has been suggested to improve the visibility of themarkings by forming them of a luminescent material, as for example, inU. S. Pat. No. 3,488,498. However, since such prior art devices relyupon ambient ultraviolet light to excite the luminescent material, theyhave only met with partial success.

SUMMARY OF THE INVENTION In view of the above, it is the primary objectof the present invention to provide an improved rear screen projectiondevice having a screen with fixed markings thereon independent of theprojected image with means for improving the visibility of the markingswithout detracting from the resolution of the projected image orinterfering with any portion of the image. A further object of thepresent invention is to provide such means which may readily be adaptedto presently existing rear screen projection devices at a minimum ofcost and expense. 7

A still further object of the present invention is to provide a methodfor improving the visibility of fixed markings on the screen of a rearprojection device without detracting from the resolution of theprojected image.

The above and other beneficial objects and advantages are attained inaccordance with the present invention by providing an improvedprojection device of the type adapted to project an image on the rearsurface of a screen for viewing from in front of the screen withreference markings on the front surface of the screen formed of aluminescent material such as an ink or paint. The invention furtherincludes a nonvisible light source mounted with respect to the device sothat at least some of the nonvisible light rays are directed at themarkings causing the same to glow. This will materially improve thevisibility of the markings without at all detracting from the resolutionof the projected image since the nonvisible light will not effect thepro- 2 jected, visible image. By forming the markings with a transparentor translucent ink, paint, or dye, the reference marks will notinterfere with the projected image.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawing:

FIG. 1 is a schematic representation of a rear screen projection devicein accordance with the present invention; and

FIG. 2 is a representative plan view of the screen of the device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Reference is now madeto the drawings and in particular to FIG. 1 wherein a typical rearscreen projection device, a shadow graph, in accordance with the presentinvention is schematically shown. The shadow graph 10 comprisesessentially a bulb 12, a set of lenses 14 and 16, a mirror 18, and ascreen 20. The components are contained in a suitable light tighthousing which includes a platform or the like to receive and position anobject 22 between the lenses as shown. The component's are furtherarranged so that when object 22 is suitably placed between the lenses,the shadow of the object is projected onto the rear of screen 20. Byproperly designing screen 20 in any one of many ways that are well knownin the art, such as by frosting screen 20, the shadow may be viewed fromthe front of the device. Further, by properly designing and positioningthe lenses with respect to the object and mirror, a magnified image maybe obtained.

Shadow graphs of the type described above are widely used in industry ascomparators for use in comparing object 22 to some fixed reference. Asan example, the shadow graph may be used to check the pitch on a threadscrew or gear tooth. To this end, a transparent overlay 23 with thedesired reference characteristics is provided over the front surface ofscreen 20. Printed on the overlay are the referencing markings to whichthe object is to be compared. FIG. 2 is a very simplified front view ofa typical comparator application wherein the image 26 of object 22 isbeing compared to reference marks 28 on overlay 23, in this case tocheck the length of the object.

Because image 26 is projected from the rear of the overlay, it should beapparent that any direct visible lighting directed at the overlay toimprove the clarity of the reference markings 28 would adversely effectthe resolution of the projected image. Further, it should be apparentthat if the reference line directly overlies the image, a portion of theimage will be occluded if the reference line is formed of an opaquematerial as is the usual custom.

For these reasons, in accordance with the present invention, themarkings 28 are formed with a transparent or translucent luminescentpaint or ink. Such paints are commercially available from a large numberof manufacturers and are produced in a wide range of colors. A varietyof such inks and paints are marketed under the trademark DAY-GLO. Theseinks are clearly visible in ordinary light and also have the capabilityof glowing under the influence of light rays including both visible andnonvisible light such as ultraviolet or blacklight. In addition, thetransparent inks allow the entire image to be seen through the ink. Thisfeature is especially useful where the overlay or template 23 is notfixed and must be positioned with reference to a particular portion ofthe projected image.

The present invention also contemplates the provision of a source 30 ofnonvisible light directed at the front of the screen so as to cause themarkings to glow independently of the rear screen projecting light. Thisglowing enhances the visibility of the markings without at alldetracting from the resolution of image 26.

Although it is desirable to protect the shadow graph screen with overlay23, this is not absolutely necessary and, the markings 28 may be applieddirectly to the screen. However, in practice, such overlays are usuallyused so as to enable the same shadow graph to be used for a wider rangeof purposes and also to protect the front of the screen. The overlay isformed of a transpar ent plastic and a convenient way of applying themarkings is to first inscribe the desired pattern on the overlay andthen go over the inscribed lines with the ink or paint, removing anyexcess material which flows over the scribe marks. This method enablesthe reference marks to be readily replaced should they wear away throughuse. A diamond tipped stylus may be used for inscribing the template.

The preceding description of the preferred embodiment of the presentinvention has been directed specifically at a shadow graph typecomparator. it is to be understood, however, that the present inventionis by no means limited to such a device and, in fact, is intended toencompass all rear screen projection devices. In its broadest aspect,the present invention may be applied to all rear screen projectiondevices including various electronic instruments utilizing cathode raytubes and the present patent application is intended to cover all suchusages which fall within the appended claims.

Having thus described the invention, what is claimed 1. In a projectiondevice of the type adapted to project an image on the rear surface of ascreen for viewing from in front of the screen, the improvementcomprising at least one marking on the front surface of the screen, saidmarking being formed of a luminescent material transparent to said imagewhereby to enable said image to be viewed from in front of said device,and means for producing nonvisible light mounted with respect to saiddevice whereby at least some of the rays from said means are adapted toimpinge upon said marking causing the same to glow.

2. The invention in accordance with claim 1 wherein said light sourcecomprises an ultraviolet light source.

3. The invention in accordance with claim 1 further comprising atransparent template overlaying the front surface of said screen andsaid markings are disposed on said template.

1. In a projection device of the type adapted to project an image on therear surface of a screen for viewing from in front of the screen, theimprovement comprising at least one marking on the front surface of thescreen, said marking being formed of a luminescent material transparentto said image whereby to enable said image to be viewed from in front ofsaid device, and means for producing nonvisible light mounted withrespect to said device whereby at least some of the rays from said meansare adapted to impinge upon said marking causing the same to glow. 2.The invention in accordance with claim 1 wherein said light sourcecomprises an ultraviolet light source.
 3. The invention in accordancewith claim 1 further comprising a transparent template overlaying thefront surface of said screen and said markings are disposed on saidtemplate.